The present invention relates to a torpedo sonar apparatus comprising a plurality of electro-acoustic transducers or hydrophones and, more particularly, relates to a torpedo sonar having those transducers arranged in several zones along a hemispherical or paraboloid-shaped torpedo bow.
Two basic types of transducer arrays are used for acoustic target searching for torpedoes. The first type of torpedo sonar has its transducers located at a flattened front surface of the torpedo head. In the second type the transducers are arranged along the curved contour of the torpedo head, sometimes called a conformal array. British patent GB 2 234 815 B shows both types of arrays. In a first embodiment (FIG. 1) several transmission transducers are arranged in a narrow vertical column on a flat central front surface of a hemispherical or paraboloid-shaped torpedo head, and several reception transducers are arranged in a narrow horizontal line on the flat front surface. Both groups of transducers together form a cross-like arrangement. The vertical transmission transducer column generates a flat fan-shaped transmission beam which is broadly distributed in horizontal direction but sharply focused in vertical direction. The horizontal reception transducer line generates a flat reception diagram which is broadly distributed in vertical direction and is narrow in horizontal direction. Both, the transmission beam and the reception diagram can be tilted electronically. In a second embodiment (FIG. 5a) GB 2 234 815 B shows the transducers of said column and/or line arranged along the curved contour of the torpedo head. Further conformal arrays of torpedo sonar transducers are described in U.S. Pat. No. 3,906,431 and in German published patent application DE 33 22 246 A1.
Providing a flat torpedo front surface increases the flow resistance of the torpedo and thus requires more energy for moving the torpedo ahead through the water. However, such an arrangement of the transducers at a flat front surface essentially reduces the number of individual transducers required for generating a particular antenna pattern and facilitates the calculations for beam forming. Because of the limitations with respect to the available size of a flat front surface, the possible number of transducers is strictly limited as well. This results in a restricted angular resolution of the sonar. Furthermore, the angular range of such sonar is limited to about xc2x145xc2x0 or, if some ambiguities are acceptable, to about xc2x160xc2x0.
When using a conformal array, the streamlined contour of the torpedo head is not impaired so that the hydrodynamic resistance of the torpedo can be optimized. In addition the angular searching range of the sonar can be essentially larger than that of a flat front surface transducer array. The maximum unambiguous angular search range is about xc2x1135xc2x0, and can be extended to about xc2x1150xc2x0 if some ambiguities are acceptable. In order to achieve such wide search angles in horizontal as well as in vertical direction, a large number of individual transducers is required. The active surface of a conformal array torpedo sonar is essential larger than that of a torpedo sonar on a flattened front portion of the torpedo head. Since the active sonar surface is completely filled with transducers, a conformal array torpedo sonar needs essential more transducers than a flat-head sonar.
It is an object of the invention to combine the advantages of both types of torpedo sonars and to simultaneously minimize the number of required transducers.
It is another object of the invention to provide a torpedo sonar which has wide angular search ranges in horizontal direction as well as in vertical direction.
It is a further object of the invention to create a torpedo sonar which is useful also in deep water.
These and other objects and advantages are achieved by the invention in that a torpedo sonar comprising a plurality of acoustic transducers has those transducers arranged in several zones along the curved surface of the torpedo bow in such a configuration that a first circular transducer zone covers the vertex region of the torpedo head and a second ring-shaped transducer zone surrounds said first zone. A lateral third transducer zone is provided at each side of the torpedo yaw axis and extends from said second zone backwards but ends before reaching the great circle of the torpedo head. A lateral fourth transducer zone at both sides of the torpedo yaw axis extends between said third zones and said great circle. This configuration leads to an acceptable minimum of required transducers. For searching purposes these transducers will be passive, i.e. receiver transducers converting ultra-sound waves into electrical signals. Some of the transducers might be active, i.e. transmitter transducers converting electrical driver signals into ultra-sound waves. Other transducers might be dual function transducers, which are alternatingly used for reception or transmission.
Preferably, the lateral third zones are formed as transition zones being broader adjacent the second zone and being narrower adjacent the fourth zones so that a smooth transition appears into the width of the fourth zone. In a particular useful embodiment of the invention the first zone extends over 1.5 xcex measured from the apex of the torpedo bow, wherein xcex is the design wavelength of the sonar. Said second zone then extends from 2.0 xcex to 5 xcex, and said third zone extends to a distance of 7 xcex measured from the apex of the torpedo head, which has a hemispherical or paraboloid-shaped or otherwise steadily curved contour. If the forward-looking component of the search signal is of less importance, there might be provided no transducers in the first zone, the vertex zone. If on the other hand, active locating or tracking of targets ahead of the torpedo is required, said first zone can be provided with transmitter transducers. In cases where an extension of the horizontal search range over more than xc2x190xc2x0 is not desired, transducers in said fourth zones can be omitted or reduced by number. In other cases it can be useful to extend said fourth zones backwards beyond the great circle. For some applications it might be necessary to extend the vertical searching angular range at least in the area of small horizontal search angles. For this purpose an embodiment of the invention has a further set of two of said third-type and fourth-type zones (forming fifth and sixth zones) arranged at the top and/or at the bottom side of the torpedo. If the water surface or objects between it and the torpedo are to be searched or imaged, then it will be sufficient to provide transducers in a further third-type zone and a further fourth-type zone (fifth and sixth zones, respectively) arranged only at the top side of the torpedo.